Grinding machines are utilized to cut, grind and/or polish metals or other types of materials. Such grinding machines are widely used in industry and take the form of both rough grinding and precision grinding apparatus. Every grinding machine, regardless of type, operates in essentially the same manner, that is, a grinding wheel is applied to a workpiece and the grinding wheel is controlled to remove a predetermined amount of material from the workpiece.
In any grinding procedure, and especially in precision grinding procedures, it is critical that irregularities in the grinding procedure be detected quickly. Such irregularities include excessive or uneven wear of the grinding wheel, unexpected hardness or flaws in the workpiece and malfunctions in the grinding machine apparatus itself. Irregularities of this type are often evidenced by excessive vibration of the workpiece and/or the grinding wheel. Such irregularities, especially in precision grinding procedures, can result in damage to the workpiece which may render the workpiece unsuitable for its intended use.
One solution to the problem of detecting irregularities in a grinding procedure has been the utilization of skilled machine operators to monitor the procedure and to take preventive action upon detection of irregularities or malfunctions. The use of a machine operator to monitor work progress obviously adds large additional expense to manufacturing cost but this additional expense has often been necessary due to the complex and expensive nature of the workpiece and the danger of damage thereto.
It is therefore an object of this invention to detect irregularities in a grinding procedure and to take action in response thereto which will prevent damage to the workpiece being ground.
It is another object of this invention to detect irregularities in a grinding procedure without requiring the use of a skilled machine operator to monitor work progress.
Elimination of grinding machine operators for monitoring work progress has been accomplished in the prior art through the use of electrical or electronic control circuits to control the grinding procedures. One such control circuit is illustrated by U.S. Pat. No. 3,650,074 granted to E. A. Weinz on Mar. 21, 1972. The invention described in this patent relates to a precision grinding machine and control circuit therefor, the grinding machine being utilized to grind and polish single crystal materials such as diamonds. This patent indicates that a problem in the prior art has been the fact that while grinding single crystal material it is necessary to orientate the workpiece such that the cutting or grinding takes place along a preferred axis of the material which is in the direction of least mechanical resistance. This problem was previously overcome by employing skilled workmen to monitor the grinding process and to ensure that the grinding process was proceeding along the preferred axes.
The use of skilled workmen is eliminated by the control circuit in this patent which utilizes a vibration transducer to detect vibrations occurring during the grinding procedure. When grinding along the preferred axis of the material, grinding vibrations are at a minimum and, conversely, while grinding along a non-preferred axis, grinding vibrations are greatly increased. The transducer or pick-up device detects the vibrations occurring during grinding and this signal is transmitted to detection circuitry calibrated to rotate the workpiece being ground in response to a predetermined level of vibration. More particularly, if the piece is orientated such that the grinding is occurring along the now-preferred axis of the material, vibrations will be at a high level and will be detected by the detection circuitry. The detection circuitry, in response to this high vibration level, operates a motor to rotate a shaft connected to the workpiece. The rotation occurs at a slow rate and continues until the vibration level decreases to a predetermined safe level thereby indicating grinding along the preferred axis of the material.
The control circuit described in this patent, although providing grinding machine control, does not detect irregularities in the grinding procedure such as grinding wheel wear or malfunction of the grinding apparatus, nor does this control circuit function to prevent damage to the workpiece resulting from such irregularities. Rather, the control circuit simply detects an increase in machine vibration and rotates the workpiece in response thereto. In addition, the vibration-sensitive transducer utilized in the patent is located quite near the grinding surface area thereby subjecting the transducer to workpiece fragments from the material being ground which may damage the vibration transducer.
It is therefore another object of this invention to provide an electronic control circuit for an automatic grinding machine that will detect irregularities in the grinding procedure and, more importantly, will prevent damage to the workpiece resulting from these irregularities.
It is a further object of this invention to provide an electronic control circuit for an automatic grinding machine which is capable of detecting variations in precision grinding procedures.
It is a further object of this invention to provide an electronic control circuit for an automatic grinding machine that utilizes a transducer which is not subject to damage or reduced efficiency resulting from workpiece fragments.
It is a further and general object of this invention to provide an electronic control circuit for an automatic grinding machine which is both inexpensive and precise in operation.